The present invention relates to a video printing apparatus for forming from a color video signal color separation films and a color film which serves as a color original for forming color separation films.
Due to a remarkable development in the modern video technique and variety of printed matters, it has been desired to develop a video printing system for printing a color image of a video signal. For this purpose, it is necessary to produce color separation films or a color film by extracting a color video signal of a desired frame from the video signal supplied from a video signal source such as a video tape player, a video disc player, a broadcasting color television signal, and a color television camera. By means of such a video printing system, it is possible to remove wholly or at least partially various problems in process speed, shutter chance, shutter noise, flash lighting and low brightness which have been encountered in the known film producing method using still cameras. Further, the above video printing system can also provide novel and useful development in the printing technology. For instance, it will be possible to produce the printing color films and color separation film directly from video information recorded on video tapes and movie films. This results in that various printed matters will be able to be published in a very simple, inexpensive and prompt manner.
In a known video printing system, in case of producing color separation films from a video tape, the video tape is first set to a video tape player and images are displayed on a monitor screen in a stop or slow reproduction mode. An operator watches the monitor screen and takes a photograph of a desired image or frame with the aid of a still camera. Then, a photographic film is developed to form a color film serving as an original for printing. After that, the original color film is set in a color scanner and four color separation films of cyan, magenta, yellow and black are formed. In such a known system, a resolution of the color film is restricted by a resolution of the image displayed on the monitor screen. In NTSC color television broadcasting system, one frame image is consisted of 525 scanning lines in regardless to a size of the image. Therefore, the resolution of the displayed image is inferior to usual color films and thus, when a photograph of the displayed image is taken by the still camera, the scanning lines are clearly recorded on the film as transverse lines. These lines might cause Moire fringes in a printed image. Therefore, it is necessary to remove the image of the scanning lines. To this end it has been proposed to expose a few frames of the continuous image reproduced in the slow mode onto a single photographic film and to make an objective lens of the still camera to be slightly out of focus. However, by means of such measures, it is impossible to obtain a photograph of a desired single frame having a sharp image. Further, in case of taking a photograph of a desired single frame of a series of images of an object moving rapidly, it is necessary to reproduce the relevant frame in the stop reproduction mode. In usual 3/4" VTR, only the image signal of a single field is reproduced in the stop mode and thus, a vertical resolution of the displayed image is reduced by two times. Therefore, it will be further difficult to remove the spaces between successive scanning lines. In view of the problems mentioned above, in the known system, a size of the image displayed on the monitor screen has to be reduced to such an extent that the scanning lines are no more distinguished and the thus reduced image is recorded by the still camera on a very small film. In such a system, the quality of the recorded image becomes too low to form a large size print more than A6 or A7 size. Further, it is difficult or inconvenient to treat such small size color films in page layout, edition, etc.
In an image processing field, it has been known to increase the resolution of images by effecting an interpolation. This technique may be advantageously applied to the above explained video printing system. In case of effecting the interpolation, the image signal of an extracted frame is once stored in a frame memory and the interpolation is carried out, while given contents stored in the frame memory are selectively read out. In this case, in order to perform any high grade interpolation, it is usual to use an electronic computer, because complicated calculation must be effected. Then a time necessary for effecting the calculation is liable to be long very much and successive signals of picture elements, i.e. pixel signals can only be obtained with a very long time interval. Usually, the operation speed of the color scanner for producing the color separation films is rather slow and four color separation films can be simultaneously formed within about forty to one hundred seconds. Therefore, if the number of interpolated pixels of the frame is about one and a half millions, there is about 27 to 67 micro seconds for obtaining the interpolation pixel. This interpolation time is rather long and use may be made of the computer, if any. Contrary to this, in a color photographing device for producing the color film, use is generally made of a cathode ray tube for displaying the image to be photographed. In the cathode ray tube, in order to keep a deflection distortion within an admissible value, a scanning speed could not be made slower than a certain limit. That is to say, the scanning speed of the cathode ray tube could not be made such a slow speed as forty to a hundred seconds per frame. In practice, it is quite difficult to solve the above mentioned two contradictory problems. Under such circumstances, in a known video printing system use is made of the simplest interpolation such as deriving an average between adjacent scanning lines as disclosed in UK Patent Application Laid-Open Publication No. 2,054,315 published on Feb. 11, 1981. In such a system, the number of scanning lines is increased only by two times and thus, the scanning lines are still perceptible. This results is that in the known system the spaces between successive scanning lines must be removed by deforming a cross section of a light spot on the cathode ray tube into an elongated circle in a direction perpendicular to the scanning line. Then, the image displayed on the cathode ray tube is also blurred and has only a lower image quality.
In order to avoid the above mentioned drawbacks of the known video printing system, one may consider to provide another frame memory after an interpolation stage. In this case, since this additional frame memory must store a very large number of picture element signals obtained after the interpolation, it must be of a very large capacity. Therefore, the whole system becomes large in size, complicated in construction and expensive in cost to a great extent.